In contrast to the extensive investigations of the past few years on group B streptococcal (GBS) polysaccharide antigens and their role in host immunity to infection, little or no emphasis has been placed on protein antigens of these bacteria. The contribution of specific protein antigenic markers (i.e. the Ibc protein components) to the virulence of the organism, to interaction with host defenses, and the role of antibody to these antigens in conferring protection against infection will be explored by a number of step-wise approaches. Meticulous characterization of many strains fo GBS of various serotypes showing the high prevalence of the Ibc protein antigenic marker has facilitated the direction of the work and will be valuable for the purification of antigens and production of monoclonal antibodies. Our findings that these antigens are naturally reeased into the culture supernatants, and that these antigens resemble each other adds to the merit of the work. The specific goals are (1) to isolate and purify the Ibc protein components (trypsin-sensitive (TS) and trypsin-resistant (TR) and to compare the antigens from strains of the major serotypes; (2) to produce mouse monoclonal antibodies and polyclonal rabbit antisera against these proteins; (3) to develop an ELISA for measuring antibody to the protein antigens; (4) to study the virulence of strains possessing these protein markers by experimental animal infections using the neonatal rat model developed in this laboratory; (5) to study the protective capacity of monoclonal antibodies to these proteins in the experimental animal model and to investigate whether immunization of a host (rat) induces protection against bacterial challenge; (6) to measure antibodies against the TR and TS antigen in the sera of mothers and infants (GBS colonized or not) and other individuals; (7) to continue studies of the interplay of these antigens with human PMN's and antibody by studies of bacterial killing, chemiluminescence and the activation of complement. Long range application of these studies include consideration of these proteins as immunogens which may even enhance the immunogenicity of GBS polysaccharide type antigens and thereby be included in GBS vaccine plans.